Acronym, meaning "laughing to keep from crying". Also a book by Langston Hughes and a national tour featuring Tyler Perry.
Best used when mocking the shenanigans of entitled white folks, particularly when said shenanigans result in the oppression, marginalization, or general disregard of people of color, the poor, the disabled, etc.
Random white person, usually via Facebook or Twitter: "I wish the old Vietnamese woman at the nail salon could draw Hello Kitty correctly."
Random white person's equally privileged and clueless friend: "They should just ship the old bitch back to where she came from."
Unlucky bystander: ltkfc